Telephone trunking system.



PATENTED MAR. 19, 1907.

H. G. WEBSTER. TELEPHONE TRUNKING SYSTEM.

"'H M I I gl M l l APPLICATION FILED AUG. 1, 1902.

UNITED STATES PATENT OFFICE.

HARRY G. WEBSTER, OF CHICAGO, ILLINOIS, ASSIGN OR TO KELLOGG SWITCHBOARDAND SUPPLY COMPANY, OF CHICAGO, ILLINOIS,

A CORPORATION OF ILLINOIS.

Specification of Letters Patent.

Patented March 19, 1907.

Application {1 August1,1902. Serial No. 117,920.

To all whom, it may concern:

Be it known that I, HARRY G. WEBSTER, a citizen of the United States ofAmerica, and a resident of Chicago, countyof Cook, and State ofIllinois, have invented a certain new and useful Improvement inTelephone Trunking Systems, of which the following is a specification.

My invention relates to improvements in telephone trunking systems, myobject being to provide a system of the kind. specified in which theoperations of connecting and disconnecting telephone-lines whichterminate at different switchboards or switchboard-sections may beconveniently and expeditiously performed.

In an application filed by Francis Dunbar August 25, 1902, Serial No.120,878, a trunking system is shown and described in which thesubscribers lines terminating at the A otlice are of the three or fourwire type and those terminating at the B ofIic-e are of the Dunbar ortwo-wire type. The operators connecting apparatus at the A office isprovided with a repeating-coil, the middle point of the windings ofwhich is connected through a supervisory relay and battery to ground.The trunk-circuit is provided at the incoming end with a trunk-relaylegged to ground through the normal contacts of a second relayresponsive to current in the line when a called subscriber responds,said trunk-relay being actuated by current from the battery associatedwith the con necting or calling ends of the A cord-circuit.

This invention relates to a similar trunking system in which lines ofthe three or four .wire type terminate at the A ofiice and lines of theDunbar or two-wire type terminate at the incoming oflice. The Acord-circuit, however, is provided with batteries bridged across eachend, one pole of which is grounded and the trunk-relay at the incomingend of the trunk is normally legged to ground from the tip side of thetrunk, the metallic circuit of the trunk being at the same time openand. a relay responsive to current in the line when thecalled'subscriber answers to disconnect said trunk-relay duringconversation and to complete the metallic circuit of the outgoing end ofthe trunk.

The invention further comprises other features of novelty, hereinafterdescribed, and

particularly pointed out in the appended claims, reference being had tothe accompanying drawing, in which the same reference charactersdesignate like parts throughout the several views, and in which Figure 1is a diagram showing the types of lines terminating at both oflices, theoperators connective circuits at the A office, and the trunk-circuitextending between the twooflices; and Fig. 2 represents a detail of thewinding of the supervisory relays used in the A cord-circuit.

The subsoribers line L, terminating at the A office, is provided at thesubstation with the usual common-battery talking instruments, includinga receiver 2 and a transmitter 4 in series between the limbs of thetelephone-line when the receiver is removed from the hook-switch 5, thelatter serving when the receiver is placed thereon to connect the tipside of the line with the grounded signaling-bell 6. The line extends intwo limbs 2 and 3 to the central office, where it is provided withmultiple connecting-jacks J and J with a cut-oil relay R, and with aline signaling device S. The jacks each have tip and sleeve springs and7' connected together and to the forward contacts of springs 7 and 8 ofthe cut-ofl relay R. A third contact 7' of each of the jacks is adaptedwhen a plug is inserted in the jack to ground the conductor 9, leadingto one side of the cut-off relay R, the other side of which is connectedby conductor 10 with the live pole of battery B, associated with thecordcircuit. The jacks are also provided with test-terminals 7",insulated from the line conductors at all times, even duringconversation, which are connected by a conductor 11 with the forwardcontact of spring 12 of the cutoff relay R, the said spring beinggrounded through a resistance 13. 'The normal contact and spring 8 ofthe cut-oif relay R leads by way of conductor 14 to one terminal of theline-signal S, which may be in the form of a drop, the other terminal ofwhich is connected by wire 15 with the point 16 upon the conductor 10,leading to the live pole of the battery B The cord-circuit at'the Aoffice is provided with an answering-plug P, provided with tip andsleeve contacts p and 10 the former of which is connected with thetip-strand t of ICC vided with tip and sleeve contacts connected,

respectively, with the tip and sleeve contacts 25 and s of thecord-circuit, which likewise include the differential windings of thesupervisory relay R and are connected together by the windings to and wof the repeatingcoil W and the battery B The windings w and tu of therepeating-coil W, as well as windings and w are in inductive relation.to each other and serve to transmit voicecurrents from one path of thecord-circuit to the other. The supervisory relay R conxtrols, as shown,the supervisory signal S in posed condenser 0 the form of anincandescent lamp, a similar supervisory signal S being provided for theother half of the cord-circuit and-controlled by the relay R Theoperators receiver 17 the secondary 18 of her induction-coil, andthecondenser c are arranged to be bridged between the strands t and s ofthe cord-circuit by means of the listening-key 7c it. The primary 19 andthe transmitter 20 of her apparatus may be charged in any desiredmanner, as by a local battery or from one of the main batteries B or 13.She is also provided with a key k, by means of which her instrument maybe connected with the order wire or circuit 21, leading to the B oflice.A calling-generator 22 may be connected betweenground and the tip-strandof the cordcircuit and by means of the tip-contact of' the ringing-key kthe sleeve-contact of said key serving to connect the sleeve-strand ofthe cord-circuit to ground.

The trunk-circuit extending between the two offices is provided at theoutgoing end with jacks J and J each having tip and sleeve contacts inthe usual manner. This circuit extends in two limbs 23 and 24 to thecentral oflice C where they terminate in windings w and w of therepeating-coil WV The tip-conductor 23 is connected through the mediumof a conductor 25 with the spring 26 of the tip-relay r associated withthe incoming end of the trunk, the forward contact of which is joined bya conductor 27 with the sleeve-limb 24 of the trunk-line. The normalcontact of the spring 26 of relay r is connected by a conductor 28 toone terminal-of the trunk-relay T the other terminal of which isgrounded. The tip and sleeve strands t and s of the trunk-cord terminatein contact-surfaces p and p of the plug P and are connected together bythe windings w and w of the repeating-coil W and an inter- The relay 1*is legged to ground from the tip-strand t of the trunkcord by means of aconductor 29. A sleeverelay 1' is connected on one. side by wire 30 withthe sleeve-strand of the trunk-cord and on the other side by wire 31,leading to point 32 upon the battery-lead 33, connected with the livepole of the battery B The disconnect or guard signal S is connected inseries with the pilot-relay 1", which is connected on one side byconductor to point 34 upon the battery-lead 36. The other terminal ofthe said signal is connected by way of conductor 35 with the armature 38of the trunkrelay 1, the back contact of which is connected by conductor39 to the back contact of spring 40 of the tip-relay W, said springbeing joined by conductor 41 with the forward contact of grounded spring42 of sleeve-relay r". The forward contact of the trunk-relay is joinedby wire43 with the back contact of spring 42 of relay 1.

A ringing-lamp S is provided for the incoming end of the trunk, saidlamp being connected on one side by conductor 33 from the live pole ofthe battery B and on the other side by conductor 44 with the backcontact of the armature of a locking-relay r and thence by way ofconductor 45 with the point 46 upon the conductor 41. The lockingrelay1" is connected on one side by con-- the forward portion of thetip-strand of the trunk-cord is connected with the spring 52 of thesleeve-relay 1*", which serves when the said relay is actuated tocomplete the strand for talking purposes, but normally to complete atesting-circuit from said spring 52 over conductor 53 to the test-relayr ,-the other pole of which is grounded by conductor 54.

The armature of said test-relay closes upon its forward contact a shuntof the operators transmitter 55, which causes a flow of current throughthe primary of her inductioncoil 56 to thereby cause a click in herreceiver 57, the latter being connected together with the secondary ofher induction-coil and the condenser c in series in the order-circuit21. A condenser c is included in the operators transmitter-circuit, aswell as the retardation-coil 58, which is connected by a conductor 59with the point 60 upon the battery-lead 36. for selectively calling thesubscribers, said means including a generator 61, adapted to beconnected by the tip-contact of key k through resistancedamp 62 with thetipstrand of the cord-circuit and the tip side of the line, thesleeve-contact of said key k The trunk-cord is provided with meansserving at the same time to close battery upon the sleeve-strand of the.trunk-cord. By means of the sleeve-contact k of the ringingkey thegenerator is connected between the ground and the sleeve-strand of thecord-circuit to direct pulsating current over the sleeve side of theline, the corresponding tipspring serving at the same time to ground thetip side of the line. The line-circuit shown at this ofiice is of theDunbar or twowire party-line type and is furnished at the central officewith the line-signal S actuated by line-relay R and a cut-off relay Rlegged to ground from the sleeve side of the talking-circuit, themultiple jacks J and J being normally disconnected from the line by saidcut-ofi' relay. The line limbs 2 and 3 extend to the substations and areconnected together when the receiver 2 is off the hookswitch 5 throughthe transmitter 4. and a retardation-coil 63, the bell 6 and a condenserbeing connected to ground from the proper side of the line when thereceiver is placed upon the hook.

The subscriber upon the line L takes. up his receiver to call thecentral oflice, and thereby closes a circuit from the battery B throughthe line-signal S, actuating the same i e test-rings 3' of the jacks areconnected through ground to the spring 12 of the cut-off relay. Currentnow flows over the metallic circuit of the connecting end of the cordand the subscribers line and through both coils of the differentialsupervisory relay R which is so arranged as to not actuate its armatureunder these conditions, whereby the supervisory signal S remains inert.The super visory signal is wound as shown more clearly in Fig. 2, inwhich the windings are shown superposed, whereby the effects of therapidly-alternating voice-currents are completely neutralized andtransmission thereof is not affected. The operator after connecting hertelephone to the cord-circuit and ascertaining the number of the wantedsubscriber depresses the key 76 and communicates with the o erator atthe B exchange,

who nominates t e trunk to be used and at the same time tests thecondition of the wanted line andif found idle inserts the plug of thetrunk.

In case the subscribers line has been connected with at some othersection, as by means of a trunk-cord of the type shown, it will be seenthat the sleeve side of the line is connected by means of the live poleof the the sleeve side of the line-circuit is connected with livebattery. When, therefore, the line is tested by means of the trunk-plug,a complete circuit is established over the forward portion of thetip-strand and through the testrelay 1" to ground. This relay being ofhigh resistance and impedance, current upon the line is not varied tosuch an extent as to disturb the connected subscribers.

In case the line is found idle the plug is inserted, which actuates thesleeverrelay r by current from battery B over conductor 33 to point 32,thence by conductor 31 through the relay 1", conductor 30, and over thesleeve-strand. s of the trunk-cord and through the cut-off relay r ofthe subscribers line to ground. The cut-off relay is thus actuated torender the signaling device inoperative and to connect the. jacks withthe limbs of the line.' At the same time the sleeve-relay r is energizedand closes a circuit of the ringingdamp S from the live pole of thebattery B over conductor 33 7 through the lamp 8, conductor 44, backcontact and armature of locking-relay r conductor 45 and 46, and thenceover conductor 41 and spring 42 of relay 1" to ground. This lamp istherefore li hted and indicates to the B operator that t e calledsubscriber has not responded. As soon as the A operator is notified asto the trunk to be used she inserts the plug P of her cord-circuit inthe jack of the trunk at her section, this occurring at substantiallythe same time that the trunk-plug P is connected with the called line. Apath for current is provided from the battery B of the A cord over thetipstrand of the cord-circuit through one winding of the supervisoryrelay R tip-conductor 23 of the trunk, through winding w of therepeating-coil W and over conductor 25,

spring 26 of relay r and conductor 28 to the trunk-relay 1' and ground.The supervisory relay R is therefore actuated and closes the circuit ofsupervisory signal S to indicate to the A operator that the calledsubscriber has not yet responded. A trunk-relay at the same time opensthe circuit of the disconnecting-lamp S, and thereby prevents its operation.

In calling the wanted subscriber the B operator depresses the contacts kk of the ring ing key or contacts 7c 7r thereof to connect the generator61 with the proper line conductor, to thereby actuate the groundedcallbell. When the called subscriber removes his receiver from the hookin answer to his call, a path for current from the battery B is providedover the metallic circuit of the line and through the tip-relay 1", thusactu- &

Spring 40 of tip-relay r at the incoming oflice initially closes thecircuit of the lockingrelay 1" from the live pole of battery B overconductor 33 to point 48, conductor 47, relay 1", conductor 49, forwardcontact and spring 40 of tip-relay r conductor 41, forward con-- tactand spring 42 of the sleeve-relay r to ground. This actuates thelocking-relay r to open the circuit of the ringing-lamp S and to closethis latter path from point 50 upon the conductor 49, over conductor 51,the for ward contact and armature of the relay, and thence overconductors 45 and 41 to the grounded spring 42 of relay W. This lamp istherefore prevented from operation during the remainder of theconnection or until the plug P is taken down and the sleeve-relay rdeene'rgized.

The subscribers are nowin communication, the battery B furnishingcurrent to the line L for talking purposes as well as for the operationof the several relays, and the battery B sending current to the calledline for talking and for the operation of the relays associated with theincoming end of the trunk. At the termination of the conversation thesubscriber upon line L returns his receiver to the hook, and therebycompletes a path from the live pole of the battery B over the tipstrandof the trunk-cord, through one winding only of the differentialsupervisory relay R and over the tip-conductorpf the sub scribers lineto ground. The supervisory sig nal S is therefore operated. The calledsubscriber in hanging up his receivenbreaks'a path for current over themetallic circuit and through the tip-relay ritherebyopening the metalliccircuit of the outgoing end of the trunk and completing a path to groundover the tip side and through the trunk-relay 1, whereby the supervisoryrelay R is actuated to operate the signal S The A operator uponobservingbothsignalslightedwithdraws the cord-plugs and takes down theconnection, with the result that the trunlcrelay r is deenergized, thusclosing the circuit of the disconnect-lamps S and the pilot-relay r, thelatter serving to operate the pilotsignal S. This circuit may be tracedfrom the live pole of the battery B over conductors 36 and 34,pilot-relay r disconnect-signal S ,'conductor 37, spring 38 and backcontact of trunk-relay r conductor 39, back contact and spring 40 oftip-relay r conductor 41.,

the forward contact and grounded spring 42 of sleeve-relay r Thedisconnect-signal indicates to the B operator the termination of theconversation, when the trunk-plug is taken down and all parts restoredto normal 1 position. The signal S serves also as a guard-signal in caseconnection is established at the outgoing end with the wrong trunk, thepath for current through the signal S being in such case over conductor36 to point 35, con- 1 ductor 34, pilot-relay r guard-signal 8 ,0011-ductor 37, spring 38, and forward contact of trunk-relay rficonductor43, back contact and grounded spring 42 of the relay 1". The

order-circuit 21, as is indicated by thei branching lines 21 connectsthe B operator with several A operators either at the same or atdifferent exchanges. The A opera tor is also provided with a pluralityof keys 762 to connect herself with the different B opl erators. Thetest-relay and the pilot-relay are of course common to a plurality ofcircuits.

Although I have described the method of making connections through themedium of i the ordercircuit, I do not wish to so confine the inventionfor it is apparent that the A operator is able to test the condition ofthe several trunks before her until an idle trunk is found, and upon sofinding a trunk she may insert the calling-plug 1 of her cordcircuit ina jack of the trunk, with the result that the trunk-relay r operates andlights the lamp S which in this method of con as before described. Itwill also be understood that had the subscriber A called for a.

connection with another subscriber in the same exchange the line of thatsubscriber would have been tested in the ordinary manner by means ofvthe cordplug P and the subscriber wouldhave been called by theringing-generator g;

The ground connections at each central office heretofore referred to, itwill be under stood, may be and in practice usually are, one and thesame, or they may be the common ofiice return.

Having thus described my invention, what I claim, and desire to secureby Letters Patout, is

1. The combination with a trunk-circuit adapted to connecttelephone-lines together for conversation, of a supervisory signalassociated with the outgoing end of the trunk placed in condition tooperate by current over the tip side only of the trunk when connectionis established at said end, and a relay at the incoming end of the trunkresponsive to current in the line when the called party answers, saidrelay adapted when actuated to disconnect the trunk-relay from the trunkand to permit a flow of current over both sides of the trunk to therebyrender said signal inoperative, substantially as described.

2. The combination with a trunk-circuit adapted to connecttelephone-lines together for conversation, of a supervisory signalassociated with the outgoing end of the trunk placed in condition tooperate by current over the tip side of the trunk and ground, themetallic circuit of the trunk being open, and a relay at the incomingend of the trunk responsive to current in the line when the calledsubscriber answers, said relay serving 'to disconnect the ground fromthe trunk and to complete the metallic circuit thereof and therebypermit a flow of current over both sides of the trunk to render saidsupervisory signal inoperative, substantially as described.

3. The combination with a trunk-circuit adapted to connecttelephone-lines together for conversation, of a supervisory signalingdevice associated with the outgoing end of the trunk having twodifferential windings placed in opposite sides of the talking-circuit,means for including one of said windings and the source of current in acircuit over the tip side of the trunk and ground when a connectionexists at the outgoing end, and a relay at the incoming end responsiveto current in the line when the calledparty answers to disconnect theground at said end and complete the metallic circuit of the trunk topermit a flow of current over both sides of the trunk and through theother winding also of the differ ential supervisory signaling devicewhereby the signal is rendered inert, substantially as described.

4. The combination with a trunk-circuit adapted to connecttelephone-lines together for conversation, of a relay at the incomingend actuated over a portion of the talking circuit when a connection isestablished with the called line, a trunk-relay at said end aotuated bycurrent over the tip side only of the outgoing end of the trunk when theconnection is established at the outgoing end, a relay at the incomingend responsive to current in the line when the called subscriberresponds, said relay being adapted when actuated to disconnect thetrunk-relay, and a signal at said end whose actuation depends upon saidrelays, substantially as described.

5. The combination with a trunk-circuit adapted to connecttelephone-lines together for conversation, of a guard-signal at theincoming end of the trunk, a relay actuated over the tip side only ofthe outgoing end of the trunk-circuit when a connection is establishedat said end to place said signal in condition to operate, and a secondrelay at the incoming end actuated by current over a portion of thetalking-circuit when a connection is established at the called line torender said signal inoperative, substantially as described.

6. The combination with a trunk-circuit adapted to connecttelephone-lines together for conversation, of a signal at the incomingend, a relay actuated over a portion of the talking-circuit whenconnection is established with the called line and a trunk-relayactuated over the tip side only of said end of the trunk when connectionis established at the outgoing end and when the called subscriberstelephone is not in use, said relay serving to control said signal sothat a guard indication is given when the trunk-relay is energized andthe first-named relay is deenergized and a disconnect indication isgiven when the first-named relay is energized and the other relay isdeenergized and the called subscriber has returned his receiver to itshook, substantially as described.

7. The combination with a trunk-circuit extending between differentswitchboardsections, of a signal at the incoming end thereof displayedwhen connection is made with a called line, of a trunk-relay at saidincoming end operated by current over one limb only of the trunk when aconnection is established at the outgoing end of said trunk to rendersaid signal inoperative, a supervisory signal associated with theoutgoing end thereof placed in condition to operate by current over thetip side of the trunk and through said trunlerelay, and means operatedwhen the called subscriber responds to disconnect said trunk-relay fromthe trunk and to render the latter signal inoperative, substantially asdescribed.

Signed by me at Chicago, county of Cook, State of Illinois, this 28thday of July, 1902.

HARRY G. WEBSTER.

WVitnesses ROBERT LEWIS AMES. F. W. DUNBAR.

